1. Field
The following description relates to a switch control technology and to a switch control circuit, method, and a converter using the switch control technology and capable of controlling a stable average current in Continuous Current Mode (CCM) regardless of an input change, a load change, or a switching off-time.
2. Description of Related Art
A power supply is an apparatus that supplies a power to a load. A buck converter is a voltage step down and current step up converter. For example, when a buck converter is used as a type of power supply, a buck converter corresponds to a step-down DC-DC converter. That is, such a buck converter is a converter that outputs a voltage that is lower than an input voltage. The buck converter uses an inductor and two switches, for example, a transistor and a diode, where these switches control the inductor to repeatedly perform a procedure of storing energy in an inductor and a procedure of discharging the stored energy from the inductor into a load.
A linear regulator may be used to lower the voltage of a DC power supply. However, the linear regulator has an issue that waste of energy is high because of an extra power being transformed into waste heat. Meanwhile, when the buck converter is implemented as an integrated circuit, the buck converter is frequently used because at least 95% of source power can be converted. Hence, wasted power is kept relatively low.
The buck converter coupled with a Light Emitting Diode (LED) includes a switch controlling the current flowing into the LED, a sensing circuit that measures the load current, where for example the sensing circuit is series-coupled to the LED and an inductor, and a control circuit controlling the switch based on the measured load current to control that constantly maintains a load average current.
Certain technologies relate to average inductor current mode switching converters and other technologies relate to a control circuit and a method for regulating an average inductor current in a switching converter. These technologies disclose a control circuit controlling a load current on a power supply.
FIG. 1 illustrates a waveform diagram of a control switch current controlled by a control circuit.
Referring to FIG. 1, an x-axis represents a time and a y-axis represents an amplitude of a current.
Such a control circuit measures a current flowing into a load through a sensing circuit and stores a time when the sensed current reaches a predefined reference current REF. For example, a control circuit stores a reach time T1, where the reach time T1 indicates a time from when a switch controlling a current is turned on to when the sensed current reaches the predefined reference current REF.
The control circuit of this example counts a reach time T1 stored at a time when a sensed current reaches the predefined reference current REF and turns off a switch at an elapsed time T2 as a reached time. Thus, the average current of a such a load current is maintained at a predefined reference current REF.
In such a control circuit, a load current is assumed to constantly increase. However, when the load current does not constantly change in such a manner, the circuit has an aspect that it is difficult to control the average current so that the average current is the same as the reference current.
Also, this control circuit includes an intermediate operational circuit for determining a reach time when the sensed current reaches the reference current and storing the determined reach time. Therefore, such an example has issues that a delay time for a current control is involved and it is difficult to control the average current according to a change of the input power and the load to achieve successful operation of such a control circuit.